Problem: Evaluate the following expression when $d = 3$ and $c = 1$. $8$ $d$ $ + 7$ $c$ $ + 9$
Explanation: Substitute $3$ for ${d}$ and $1$ for ${c}$ $ = 8{(3)} + 7{(1)} + 9 $ $ = 24 + 7 + 9 $ $ = 40$